1. Field of the Invention
The present invention relates to power supplies and, more specifically, to an uninterruptible power supply.
2. Description of the Prior Art
Computers, such as personal computers, often face power problems from the main alternating current (AC) power supply such as blackouts (total losses of power) and brownouts (very short interruptions), spikes, transients, sags, surges and various types of noise. Such problems cause considerable damage to computer systems, including system lock-ups and complete corruption or loss of data. Many computers employ uninterruptible power supplies to ensure trouble-free operation.
Existing uninterruptible power supplies use a battery to provide power during blackouts and other transients. An inverter transforms the direct current (DC) from the battery to alternating current having characteristics similar to the current produced by the main AC power supply. Inverters, however, have relatively high failure rates due to the type and number of components that they employ.
Therefore, there is a need for an inverterless uninterruptible power supply.
The disadvantages of the prior art are overcome by the present invention which, in one aspect, is an inverterless circuit for an uninterruptible power supply that includes a battery. A clock circuit generates a first periodic signal having a first frequency. An AC supply detection circuit generates a line control signal that is un-asserted when an AC supply is capable of supplying power above a predetermined threshold and is asserted when the AC supply is not capable of supplying power above the predetermined threshold. A control gate is responsive to the first periodic signal and to the line control signal. The control gate generates a power control signal. The power control signal is a periodic signal having the first frequency when the line control signal is asserted and is zero when the line control signal is un-asserted. A power transistor is gated by the power control signal, and periodically transfers current from the battery to the load at the first frequency.
Another aspect of the invention is a method of providing power to a load from a battery. A voltage of an AC power supply is sensed. A line control signal is asserted when the voltage is below a predetermined threshold. A plurality of periodic pulses is generated. The plurality of pulses is AND""ed with the line control signal, thereby generating a pulsed signal when the voltage is below the predetermined threshold. A power transistor is gated with the pulsed signal. The power transistor is capable of electrically coupling the battery to the load,.
These and other aspects of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the following drawings. As would be obvious to one skilled in the art, many variations and modifications of the invention may be effected without departing from the spirit and scope of the novel concepts of the disclosure.